Outlook stopped receiving mail...

I'm running XP Pro, Outlook 2003 & have SBC Yahoo Business DSL as my
ISP.
I'm using outlook with my sbcglobal.net email & on Thursday, I stopped
receiving emails to Outlook.
They still come to iPhone & everything is current when going to the
webmail page.
I can test the account settings in Outlook & everything works just
fine - test email goes everywhere its supposed to, except for Outlook!
I have created a new profile, new email account, pst file, using
different combinations of each, all with the same result.
Error messages I am getting are;
'Receiving' reported an error (0x800CCC90) : Your incoming (POP3)
email server has reported an internal error. If you continue to
receive this message, contact your server administrator or ISP. The
server responded ; ERR inactivity time out.
I've also received the message that the connection to the server was
interrupted, with the error code (0x800CCC0F).
Server time out is set to 10 minutes.
I have also gone to webmail & taken every message from the time this
started to present time & moved them to a separate folder, thinking an
email message may have been causing it.
I have also disable NAV, thinking it may be part of the problem, but
no luck.
ATT's tech support is pretty useless, as 'they don't support' Outlook!
One last thing, another user in office is having no problems, the only
difference is that she's using Outlook Express.
Any suggestions?
Thanks!